is there a formula that sum only for direct children

if I have a project and this project has task and the task have sub task

the hierocracy will be the project is the parent, the task will be children for the project, the sub task will be children for task

I want a formula that I apply in the project row that is going to sum the utilization percentage from tasks only "direct children" and the same for task, it should only look for the sub task utilization underneath it